The ornamental design for a side body for an automobile, as shown and described.
FIG. 1 is a front perspective view of a side body for an automobile showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a right side view thereof, the left side view being a mirror image.
The claimed design is indicated by the relatively dark portions in the figures, while the relatively light portions are environmental and form no part of the claimed design.